This invention relates to a dispensing head for depositing layers of solidifying material in a desired pattern to form three-dimensional physical objects. One useful application for such a device is rapid prototyping of models or objects. The modeling material is selected and its temperature is controlled so that it solidifies upon extrusion from the dispensing head onto a base, with the build-up of multiple layers forming the desired article.
A rapid prototyping system involves the molding of three-dimensional objects based upon design data which is provided from a computer aided design (CAD) system. Examples of apparatus and methods for rapid prototyping of three-dimensional objects by depositing layers of solidifying material are described in Crump U.S. Pat. No. 5,121,329, Batchelder et al. U.S. Pat. No. 5,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder U.S. Pat. No. 5,402,351, Batchelder U.S. Pat. No. 5,426,722, Crump et al. U.S. Pat. No. 5,503,785, and Abrams et al. U.S. Pat. No. 5,587,913, all of which are assigned to Stratasys, Inc. The rapid prototyping systems disclosed in the '329, '433 and '785 patents ("Crump patents") describe an extrusion head which receives a solid state material used to form three-dimensional articles, heats the material to just above its solidification temperature, and dispenses the material as a fluid onto a base.
Various embodiments of the extrusion head are shown in the Crump '433 patent. Each embodiment includes a liquifier which consists of three zones: an entrance zone or cap, a heating zone or body and a nozzle. A first embodiment is shown in FIG. 3 of the '433 patent. FIG. 3 shows a liquifier within a extrusion head having a seal ring (i.e., a cap), a heating head (i.e., heating zone) and a nozzle. The seal ring receives a supply rod of solid material. An electric heater within the heating head heats the supply rod to a temperature exceeding its solidification temperature, reducing it to a liquid state. The liquid material then flows into the nozzle through a nozzle flow passage, and is dispensed through a nozzle dispensing outlet.
A second embodiment of the extrusion head is shown in FIG. 5 of the Crump '433 patent. In this embodiment, the supply material is in the form of a flexible strand in solid form. The flexible strand of material shown in FIG. 5 is fed through a guide sleeve to a extrusion head. The extrusion head contains a supply chamber in a top portion and a liquifier in a bottom portion. Drive rollers within the supply chamber introduce the flexible strand into the liquifier. The liquifier within the extrusion head includes a seal ring (i.e., a cap), a material supply and flow passage (i.e., heating zone) and a dispensing outlet orifice (i.e., a nozzle). The flexible strand is advanced into the liquifier through the seal ring, which provides a hydraulic seal around the internal surface of the flow passage. A heater in the form of a sleeve containing a heating coil is positioned around the flow passage and the orifice to heat the strand to a fluid state in the passage. The material is dispensed in a fluid state through the orifice.
A third embodiment of the extrusion head is shown in FIG. 13 of the Crump '433 patent. As with the embodiment shown in FIG. 5, the material is supplied in the form of a flexible strand in solid form. The strand is advanced into a extrusion head through a guide sleeve. A strand advance mechanism comprising a pair of motor-driven feed rollers or pullies and advances the strand into the liquifier. The liquifier of FIG. 13 is comprised of a tubular guide member, a seal ring, a liquifier nozzle and a removable tip. The tubular guide member and seal ring together form the cap zone. The tubular guide member is made of highly conductive metal, such as aluminum or silver. It dissipates heat rapidly to maintain the flexible strand at a suitable temperature during its movement from the strand advance mechanism into the heating zone. To further dissipate heat from the guide member, a blower may be used to circulate air into the extrusion head, around the guide member. A cooling fin extending from the guide member in an "L"-shape is additionally utilized to enhance the heat dissipation from the guide member. At its lower end, the guide member is supported on the seal ring. The seal ring is made out of heat-insulating plastic to serve as a thermal seal. The liquifier nozzle surrounded by a heating coil and an outer insulation sleeve provides a heating zone in which the strand material is melted. The liquifier nozzle (i.e., heating tube) is made of heat-conducting material such as silver or preferably aluminum. The removable tip is attached to the bottom end of the liquifier nozzle by a threaded connection.
A fourth embodiment of the extrusion head is shown in FIG. 6 of the Crump '433 patent. In this embodiment, multiple materials are dispensed through separate passages into a single discharge outlet. The embodiment of FIG. 6 allows utilization of different materials to form different layers of the same article.
The Crump '785 patent discloses an extrusion head carrying two liquifiers, each having its own nozzle. The liquifiers of the '785 patent each have a cap at a receiving end, secured by a mounting ring to a tubular dispenser (i.e., heating tube). A heating coil is wrapped around each tubular dispenser to heat and melt a filament of material. In each liquifier, the material is provided in a fluid state to a dispensing nozzle and discharged through a nozzle tip. Filament is conveyed to each liquifier from a supply spool by a pair of pinch rollers driven by stepper motors.
In the aforementioned liquifiers, the cap region serves as the transition zone for the modeling material where at the entrance to the cap the temperature is below the softening point of the material and the outlet of the cap is above the temperature required to pump the material in a semi-liquid state. This requires a change in temperature of up to 250.degree. Celsius over the length of the cap. Ideal properties for the cap are a high thermal resistivity in the axial direction and low thermal resistivity in the radial direction. The previous designs, such as those described in the Crump patents, used high temperature thermoplastics or thermoset plastics such as Dupont "Vespel" SP-1, for the cap to accomplish these goals. These caps are expensive, have temperature limitations, and require a sealing mechanism between the cap and the heating body, which is typically formed of aluminum. The caps and seal are prone to leakage.
It would be desirable to form the cap zone of the liquifier out of the same medium used to form the liquifier body. A medium that is inexpensive, that allows bends in the liquifier path to be easily made, and that can further be used to form the nozzle zone would also be desirable.